Upon consultation between the members of the Epidemiology Branch of NCI and the members of the Immunodeficiency Registry, it was decided that a collaborative program between these two parties should be developed. The goals of this collaborative program would be as follows: to continue the registry's activities as outlined above; to explore in a feasibility study two additional activities; and to conduct these activities, if deemed feasible. The two additional activities are: to determine better estimates than are currently available of the prevalence of immunodeficiency syntromes by types, age, and sex in general population (the feasiblity of an incidence survey would also be explored at this time); and to conduct a case-control study of the clinical, demographic, and laboratory characteristics of immunodeficient patients who developed a malignancy vs. those who didn't.